trezor-firmware/trezorlib/transport/__init__.py

# This file is part of the Trezor project.
#
# Copyright (C) 2012-2018 SatoshiLabs and contributors
#
# This library is free software: you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License version 3
# as published by the Free Software Foundation.
#
# This library is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the License along with this library.
# If not, see <https://www.gnu.org/licenses/lgpl-3.0.html>.

import importlib
import logging
from typing import Iterable, Type

from ..protobuf import MessageType

LOG = logging.getLogger(__name__)


class TransportException(Exception):
    pass


class Transport:
    """Raw connection to a Trezor device.

    Transport subclass represents a kind of communication link: Trezor Bridge, WebUSB
    or USB-HID connection, or UDP socket of listening emulator(s).
    It can also enumerate devices available over this communication link, and return
    them as instances.

    Transport instance is a thing that:
    - can be identified and requested by a string URI-like path
    - can open and close sessions, which enclose related operations
    - can read and write protobuf messages

    You need to implement a new Transport subclass if you invent a new way to connect
    a Trezor device to a computer.
    """

    PATH_PREFIX = None  # type: str

    def __str__(self) -> str:
        return self.get_path()

    def get_path(self) -> str:
        raise NotImplementedError

    def begin_session(self) -> None:
        raise NotImplementedError

    def end_session(self) -> None:
        raise NotImplementedError

    def read(self) -> MessageType:
        raise NotImplementedError

    def write(self, message: MessageType) -> None:
        raise NotImplementedError

    @classmethod
    def enumerate(cls) -> Iterable["Transport"]:
        raise NotImplementedError

    @classmethod
    def find_by_path(cls, path: str, prefix_search: bool = False) -> "Transport":
        for device in cls.enumerate():
            if (
                path is None
                or device.get_path() == path
                or (prefix_search and device.get_path().startswith(path))
            ):
                return device

        raise TransportException(
            "{} device not found: {}".format(cls.PATH_PREFIX, path)
        )


def all_transports() -> Iterable[Type[Transport]]:
    transports = set()  # type: Set[Type[Transport]]
    for modname in ("bridge", "hid", "udp", "webusb"):
        try:
            # Import the module and find the Transport class.
            # To avoid iterating over every item, the module should assign its Transport class
            # to a constant named TRANSPORT.
            module = importlib.import_module("." + modname, __name__)
            try:
                transports.add(getattr(module, "TRANSPORT"))
            except AttributeError:
                LOG.warning("Skipping broken module {}".format(modname))
        except ImportError as e:
            LOG.info("Failed to import module {}: {}".format(modname, e))

    return transports


def enumerate_devices() -> Iterable[Transport]:
    devices = []  # type: List[Transport]
    for transport in all_transports():
        try:
            found = transport.enumerate()
            LOG.info(
                "Enumerating {}: found {} devices".format(
                    transport.__name__, len(found)
                )
            )
            devices.extend(found)
        except NotImplementedError:
            LOG.error(
                "{} does not implement device enumeration".format(transport.__name__)
            )
        except Exception as e:
            LOG.error(
                "Failed to enumerate {}. {}: {}".format(
                    transport.__name__, e.__class__.__name__, e
                )
            )
    return devices


def get_transport(path: str = None, prefix_search: bool = False) -> Transport:
    if path is None:
        try:
            return next(iter(enumerate_devices()))
        except IndexError:
            raise Exception("No TREZOR device found") from None

    # Find whether B is prefix of A (transport name is part of the path)
    # or A is prefix of B (path is a prefix, or a name, of transport).
    # This naively expects that no two transports have a common prefix.
    def match_prefix(a: str, b: str) -> bool:
        return a.startswith(b) or b.startswith(a)

    LOG.info(
        "looking for device by {}: {}".format(
            "prefix" if prefix_search else "full path", path
        )
    )
    transports = [t for t in all_transports() if match_prefix(path, t.PATH_PREFIX)]
    if transports:
        return transports[0].find_by_path(path, prefix_search=prefix_search)

    raise Exception("Could not find device by path: {}".format(path))